A* 



LIBRARY OF 



CONGRESS 



019 410 660 9 



Hollinger 
pH 8.5 



Bulletin 3 

Structural Materials Research Laboratory 

Lewis Institute 

Chicago 



Effect of Vibration, Jigging 

and Pressure on Fresh 

Concrete 

By 

DUFF A. ABRAMS 

Professor in Charge of Laboratory 



(Authorized Reprint from the Proceedings of the American 
Concrete Institute, Vol. XV, 1919) 



Published by the 
STRUCTURAL MATERIALS RESEARCH LABORATORY 

Lewis Institute 

Chicago 

NOVEMBER. 1919 



I? ESEARCHES in the properties of concrete and concrete materials at 
the Structural Materials Research Laboratory are being carried out 
through the cooperation of the Lewis Institute and the Portland Cement 
Association, Chicago. The research work has been under way since 
September 1, 1914. 

The control of the policies of the Laboratory is vested in an Advisory 
Committee, consisting of representatives of the Lewis Institute and the 
Portland Cement Association as follows: 

Lewis Institute: 

DUFF A. ABRAMS, Professor in charge of Laboratory. 
PHILLIP B. WOOD WORTH, Professor of Engineering. 

Portland Cement Association: 

F. W. KELLEY, Chairman, Technical Problems Committee, Albany, N. Y. 
ERNEST ASHTON, Member, Technical Problems Committee, Allentown, 
Pa. 

The investigations are being carried out by a staff of engineers, 
chemists, and assistants who give their entire time to this work. The 
results of these researches are published in the form of papers before 
engineering and technical societies and in Circulars and Bulletins issued 
by the Laboratory. 



j\/» 



n 






EFFECT OF VIBRATION, JIGGING AND PRESSURE ON FRESH 

CONCRETE.* 

By Duff A. Abrams. 

Introduction. 

An experimental study of the effect of vibration and pressure on fresh 
concrete on its strength and other properties is of interest in view of the 
frequent use of such devices as hand-hammering of forms, or air-hammering, 
jigging or vibration as an aid in placing concrete. Such methods are partic- 
ularly applicable to the construction of reinforced-concrete ships and houses, 
where thin sections and a multiplicity of reinforcing members are of common 
occurrence. Jigging or vibrating machines are frequently used in concrete 
products plants. The effect of pressure on fresh concrete is of interest in 
certain problems of concrete design. 

Little attention has heretofore been given to the experimental study of 
the effects- produced by vibration and jigging fresh concrete. A few tests 
were made in a study of the effect of pressure on fresh cement paste in a 
confined space by James E. Howard, at Watertown Arsenal. 1 The effect of 
pressure on the compressive strength and bond was studied by the writer 
at the University of Illinois in 1913. 2 Since the tests reported herein were 
completed, Prof. F. P. McKibben has published a report on compression 
tests of concrete columns which set under pressure. 3 

The tests included in this report were made as a part of the experimental 
studies of concrete and concrete materials being carried out through the 
cooperation of Lewis Institute and the Portland Cement Association. 

Outline of Tests. 
The tests included in this report cover the following topics : 

1. Different methods of hand-molding of test cylinders. 

(a) Puddling with f-in. round steel bar (varying number of strokes) . 
(6) Tamping (tampers of different size), 
(c) Tapping metal forms after puddling. 

2. Effect of vibrating fresh concrete (small electric motor, Fig. 1.). 

(a) Time of vibration varied up to 1 min. 

3. Effect of jigging fresh concrete (using machine shown in Fig. 2). 

(a) Concrete of different mixes (1:7 to 1:3). 

(6) Concrete of different consistencies (0.70 to 1.25). 



* Authorized Reprint from the Proceeding of the American Concrete Institute, Vol. XV, 1919. 
1 Cement Age, June, 1905. 

* "Tests of Bond between Concrete and Steel." Bulletin 71, Illinois Engineering Experiment Station, 
1914. 

1 Eng. News-Rec, Dec. 5, 1918. 

(1) 



2 Structural Materials Research Laboratory. 

(c) Using aggregate of different grading (fineness modulus 4.00 to 

6.50). 

(d) Using aggregate of different sizes (0-28 sand to 0-lHn. concrete 

aggregate). 

(e) Using coarse aggregate of different shape (pebbles and crushed 

stone) . 
(/) Effect of rate of jigging (0 to 150 r. p. m.). 
(g) Effect of height of drop (0 to 0.50 in.). 
(h) Effect of length of time jigged (up to 3 min.). 
(i) Effect of age of concrete before jigging (up to 6 hr.). 
(i) Jigged with 30-lb. weight on top of fresh concrete. 
(k) Hand puddling on jigging machine while in operation. 
4. Effect of pressure on fresh concrete (method of applying the higher 
pressures shown in Fig. 3). 

(a) Using different pressures (0 to 500 lb. per sq. in.). 

(b) Effect of duration of pressure (15 min. to 16 hr.). 

(c) Effect of removal of water by pressure. 

This series included 900 compression tests of 6 x 12-in. concrete cylinders 
at the age of 28 days. All specimens were made from the same materials 
at the same time, consequently direct comparisons may be made between 
any two sets of tests. 

Materials. 

The portland cement used consisted of a mixture of equal parts of four 
rbrands purchased from Chicago dealers. The cement conformed to all the 
equirements of the Standard Specifications and Tests for Portland Cement of 
%e American Society for Testing Materials. 

In general the aggregates consisted of sand and pebbles from the Chicago 
Gravel Company's pit near Elgin, 111. In one group of tests crushed limestone 
was used as coarse aggregate. Sieve analysis and miscellaneous tests of 
aggregates are given in Table 1. 

The "fineness modulus" of an aggregate may be used as a measure of 
its size and grading. It is the sum of the percentages in the sieve analysis 
divided by 100. The sieve analysis is expressed in terms of weight or volume 
coarser than each sieve. Tyler standard screen scale sieves are used. The 
sizes of sieves and fineness modulus of the aggregates used in these tests are 
shown in Table 1. Low values of fineness modulus (abbreviated to F. M. in 
the tables) correspond to small size and high values to the coarse sizes of 
aggregate.* 

Test Pieces. 

All test pieces consisted of 6 x 12-in. cylinders which were stored in damp 
sand for 28 days. The concrete for each specimen was proportioned separately 
and mixed by hand with a bricklayer's trowel in a shallow metal pan. The 

•For further details on fineness modulus of aggregates see the writer's report on "Design of Concrete 
Mixtures," Bulletin 1, Structural Materials Research Laboratory. 



Effect of Vibration, Jigging and Pressure on Concrete. 3 

forms consisted of 12-in. lengths of cold-drawn steel tubing, split along one 
element. Each form stood on a machined cast-iron base plate. A smooth 
top was formed by means of neat cement and plate glass. 

Unless otherwise noted, the specimens were molded by the "standard" 
hand-puddling method before subjecting them to vibration, jigging or pressure. 
This method consists of puddling the fresh concrete in the metal form in 4-in. 
layers by means of 25 strokes with a f-in. round steel bar and leveling off 
with a trowel. This method has been in use for several years in our research 
work and has been found to give uniform results for different operators. The 
strength of the concrete produced by this method of molding is used as a 
basis for comparison (100 per cent.) for all other methods of treatment included 
in this investigation. 

Table 1. — Miscellaneous Tests of Aggregate. 



Size 


Kind. 


Weight 
lb. per 
cu. ft. 


Density. 


Sieve Analysis of Aggregate. 
(Per cent by weight coarser than each sieve.) 


Fineness 
Modu- 
lus.' 


































100 
88 


48 
42 


28 


14 


8 


4 


tin. 


fin. 


Uin. 




0-28 


) 


102 


0.61 

















1.20 


0-14 


Elgin 


104 


0.62 


90 


91 


36 


'6 












2.25 


0-8 


Sand 


108 


0.65 


99 


93 


50 


22 


'6 










2.64 


0-4 


and 


112 


0.67 


99 


94 


59 


36 


18 


"6 








3.06 


0-iin. 


Pebbles 


120 


0.72 


99 


96 


73 


57 


46 


33 


'6 






4.04 


0-f in. 




124 


0.74 


99 


97 


82 


72 


64 


58 


30 


'6 




5.02 


0-1 J in. 


I 


128 


0.77 


99 


98 


87 


80 


75 


68 


48 


20 


'6 


5.75 




f 


119 


0.71 


99 


95 


69 


51 


38 


24 


17 


7 





4.00 




f Elgin 1 


125 


0.75 


99 


97 


79 


68 


58 


49 


35 


15 





5.00 


0-U in. 


1 Sand 1 
and 1 


126 


0.76 


99 


98 


85 


76 


69 


62 


43 


18 





5.50 


128 


0.77 


99 


98 


87 


80 


75 


68 


48 


20 





5.75 




Pebbles | 


128 


0.77 


100 


98 


90 


84 


79 


75 


52 


22 





6.00 




i 


125 


0.75 


100 


99 


92 


88 


84 


81 


57 


24 





6.25 






120 


0.72 


100 


99 


95 


92 


90 


87 


62 


25 





6.50 




' 


123 


0.74 


99 


95 


69 


51 


38 


24 


17 


7 





4.00 




Elgin 


128 


0.77 


99 


97 


79 


68 


58 


49 


35 


15 





5.00 




Sand 


124 


0.74 


99 


98 


85 


76 


69 


62 


43 


18 





5.50 


0-U in. 


and 


122 


0.73 


99 


98 


87 


80 


75 


68 


48 


20 





5.75 




Crushed 


118 


0.71 


100 


98 


90 


84 


79 


75 


52 


22 





6.00 




Lime- 


114 


0.68 


100 


99 


92 


88 


84 


81 


57 


24 





6.25 




stone 


no 


0.66 


100 


99 


95 


92 


90 


87 


62 


25 





6.50 



• The sum of percentages in sieve analysis, divided by 100. 



The mixture is expressed as one volume of cement to a given number of 
volumes of mixed aggregate. A 1:5 mix expressed in this manner is about 
the same ao the ordinary 1:2:4 mix. The exact equivalent of the latter will 
vary with the size and grading of the aggregates. 

The water content of the concrete is expressed in terms of the relative 
consistency and the "water-ratio." A relative consistency of 1.00 (normal 
consistency) is of such plasticity that the concrete of usual mixes will slump 
% to 1 in. if the metal form is withdrawn by a steady upward pull immediately 
after molding the cylinder by the standard method. A relative consistency of 
1.10 contains 10 per cent more water than normal consistency. The water- 
ratio is the ratio of volume of water to volume of cement in the batch. The 



4 Structural Materials Research Laboratory. 

weight of cement was assumed as 94 lb. per cu. ft. For one mix and given 
concrete materials the relative consistency and water-ratio may be used inter- 
changeably. 

In the hand-molded specimens the method of placing the concrete was 
varied by changing the number of strokes of the puddling bar, using layers of 
different thickness, etc. Hand-tampers 2 in. and 5 in. in diameter were also 




FIG. 1. ELECTRIC VIBRATOR. 

Shows set-up for vibration tests given in Table 3. 
Motor weighed 12 lb., ran about 1000 r. p. m. 



used. In one set of tests the form was struck with a steel bar after molding 
by the standard puddling method. 

In the vibration tests the cylinder mold was bolted to a light timber 
table and the concrete specimen molded by the standard hand-puddling 
method described above. 

Violent vibration was produced by holding an electric motor frame 
against the side of the steel form as shown in Fig. 1. The motor carried an 



Effect of Vibration, Jigging and Pressure on Concrete. 5 

eccentric flywheel, weighed 12 lb. and ran about 1000 r. p. m. The time of 
vibration varied from 5 sec. to 1 min. 

The jigging tests were made on the machine shown in Fig. 2. The machine 
consisted of a framework carrying a metal table about 4 ft. wide and 8 ft. 
long weighing about 700 lb. The table was raised by means of belt-driven 
cams on two longitudinal shafts. The rate and height of drop could be varied 
over a wide range. In most of the tests the machine was run for 20 sec. at 
100 drops per min., 0.1-in. drop; however, each of these factors were varied 
with the other two constant. 

All specimens were molded by the standard hand-puddling method before 
pressure was applied. Pressures up to 10 lb. per sq. in. were applied by piling 
weights on top of a loose-fitting cover plate. Pressures of 25 and 50 lb. per 




FIG. 2. — JIGGING MACHINE. 

Steel table 4 x 8 ft.; weight 700 lb. Table raised by means of cams; rate and height of drop 
can be varied over wide range. 



sq. in. were applied by weighted levers. Pressures of 100 to 500 lb. per sq. in. 
were obtained by placing the freshly molded specimen in a testing machine, as 
shown in Fig. 3. The spring facilitated maintaining a constant pressure. 
For all pressures the time of application varied from 15 min. to 16 hr. 

The metal forms are fairly tight and permit little leakage of water under 
ordinary conditions. For the wetter concretes the joints were sealed with 
paraffin. In the pressure tests the water expelled was collected by means 
of sponges and weighed. It should be noted that this water was almost clear. 

Test cylinders were made in sets of 5 on different days. One specimen of 
each form was made before starting the second round. The strengths given in 
the tables are the average of 5 entirely independent tests. In this way minor 
variations in materials, proportions, manipulation, etc., are eliminated. In 
the case of the "standard" hand-puddled specimens which are used as a basis 
of comparison, 3 sets of 5 specimens were made in different parts of the series. 



6 Structural Materials Research Laboratory. 

Test Data and Discussion. 
Data of the tests will be found in Tables 2 to 7. Only average values are 
reported. It will be noted that the "standard" hand-puddled concrete 
(average of 15 tests) is used as the basis of comparison. The diagrams in Figs. 
4 to 16 give the data in graphical form. 




FIG. 3. METHOD OF APPLYING PRESSURE TO FRESH 

CONCRETE. 

The higher pressures were applied by means of a testing 
machine. The spring facilitated maintaining a constant 
pressure. The plate in contact with fresh concrete was 
loose-fitting. The water expelled from concrete was col- 
lected by means of sponges and weighed. 

A comparison of the relative effects of puddling 1:5 plastic concrete 
with a steel bar and tamping with tampers of different weight and size is given 
in Table 2. 

The effect of vibration with electric vibrator is shown in Table 3 and 
Fig. 4. Vibrating for about 30 seconds caused no appreciable effect on the 
strength of concrete which had been puddled in place by hand. The tests 



Effect of Vibration, Jigging and Pressure on Concrete. 7 



Table 2. — Effect of Method of Molding Concrete Specimens. 

Compression tests of 6 x 12-in. cylinders. 
Age at test 28 days; stored in damp sand; tested damp. 
Aggregate — Sand and pebbles from Elgin, 111., graded O-IJ^ in. 
Each value is the average of 5 tests made on different days. 



Kef. No. 


Mix 

by 

Volume. 


F. M. of 

Aggre- 
gate. 


1 


1:5 


5.75 


31 
51 

84 






2 






147 






148 


.... 




149 


.... 




150 






3 


.... 




4 






5 


.... 





Relative 
Consist- 
ency. 



.00 



Water- 
Ratio to 
Volume of 
Cement. 


Compressive Strength 


lb. per 
sq. in. 


Per cent of 
Standard. 


0.875 


2680 


96 




2800 
2710 
2840 


100 




2780* 


] 




2810 


101 




2690 


97 ! 




2420 


87 




2430 


87 




2500 


90 




2800 


101 




2570 


92 




2740 


98 



Treatment of Concrete 



12 strokes around perimeter 
of form for each 4-in. layer 
of concrete using f-in. 
steel bar. 

25 strokes distributed over 
section for each 4-in. layer 
using f-in. steel bar. 
(Standard method). 



50 strokes distributed over 
section for each 4-in. laye 
using f-in. bar. 

12 strokes on each 3-in. layer 
using 2-lb. tamper 2 in. in 
diameter. 

12 strokes on each 6-in. layer, 
using 2-lb. 2-in. tamper. 

12 strokes on first 3-in. layer 
using 2-lb. 2-in. tamper, 
forms then filled before 
tamping again with 12 
strokes. 

12 strokes on first 3-in. layer, 
using 2-lb. 2-in. tamper, 
remaining concrete settled 
by tapping form lightly. 

25 strokes distributed over 
section for each 4-in. layer 
with 2-lb. 2-in. tamper. 

25 strokes distributed over 
section for each 4-in. layer 
with 2-lb. 5-in. tamper. 

Standard method of molding, 
except form struck 3 light 
blows with steel bar after 
puddling each 4-in. layer. 



* Average of 15 tests made on different days. This value is used as a basis for comparison in Tables 
2, 3, 6 and 7. 



Structural Materials Research Laboratory. 



Table 3. — Effect of Vibration with Electric Motor. 

Method of vibrating shown in Fig. 1. 

Compression tests of 6 x 12-in. cylinders. 

Results of tests are platted in Fig. 4. 

Age at test 28 days; stored in damp sand; tested damp. 

Aggregate — Sand and pebbles from Elgin, 111., graded 0-1 H in 

Each value is the average of 5 tests made on different days. 



Ref. No. 


Mix 

by 
Volume. 


F.M.of 
Aggre- 
gate. 


Relative 
Consist- 
ency. 


Water- 
Ratio to 
Volume of 
Cement. 


Compressive Strength 




lb. per 
sq. in. 


Per cent of 
Standard. 


Treatment of Concrete. 


31,51,84 


1:5 


5.75 


1.00 


0.875 


2780* 


100 


Standard method of molding. 


6 










2880 


104 


Standard method of molding. 
Vibrated 5 sec. 


7 










2640 


95 


Standard method of molding. 
Vibrated 10 sec. 


8 










2830 


102 


Standard method of molding. 
Vibrated 20 sec. 













2700 


97 


Standard method of molding. 
Vibrated 30 sec. 


10 










2520 


91 


Standard method of molding. 
Vibrated 45 sec. 


11 










2470 


89 


Standard method of molding. 
Vibrated 60 sec. 



Average of 15 tests made on different days, See Table 2. 



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GO 



FIG. 4. EFFECT OF VIBRATION ON THE STRENGTH OF CONCRETE. 

Vibration produced by electric motor shown in Fig. 1. Compression testa of 6 x 12-in. cylinders 
Age, 28 days. Data from Table 3. 



Effect of Vibration, Jigging and Pressure on Concrete. 9 

Table 4.— Effect of Jigging on the Strength of Concrete. 
(Concrete of Different Mixes and Consistencies.) 
Values platted in Fig. 5. 

All cylinders were molded by the standard method before vibrating on machine shown in Fig. 2. 

(lOOr.pjn.; 0.1-in. drop; jigged 20 sec.) 
Compression tests of 6 x 12-in. cylinders. 
Age at test 28 days; stored in damp sand; tested damp. 
Aggregate — Sand and pebbles from Elgin, 111. 
Each value is the average of 5 tests made on different days. 





Mix 

by 


* Aggregate. 


Relative 
Consist- 


Water- 


Compressive Strength. 


Ref. 

No. 






Ratio to 
Volume of 
Cement. 




Standard 


Jigged 


Vol. 


Size. 


F. M. 


ency. 


Standard Method, 


Method Plus 


Concrete, 












lb. per sq. in. 


Jigging, Jb. per 


Per cent of 
















sq. in. 


Standard. 


75 


1:7 


0-1* 


5.75 


0.70 


0.757 


1270 


1560 


123 


76 








0.80 


0.866 


1650 


1910 


116 


77 








0.90 


0.974 


1730 


2000 


116 


78 








1.00 


1.081 


1710 


1800 


105 


79 








1.10 


1.190 


1480 


1460 


99 


80 








1.25 


1.353 


1140 
Av. 1500 


1110 
1640 


97 
109 


81 


1:5 


0-1* 


5.75 


0.70 


0.612 


1650 


2020 


122 


82 








0.80 


0.700 


2560 


2870 


112 


83 








0.90 


0.788 


2920 


3120 


107 


84 








1.00 


0.875 


2840 


2630 


93 


85 








1.10 


0.962 


2120 


2040 


96 


86 








1.25 


1.085 


1580 
Av. 2280 


1560 
2370 


99 
104 


87 


1:4 


0-H 


5.75 


0.70 


0.540 


1690 


2160 


128 


88 








0.80 


0.618 


3760 


3600 


96 


89 








0.90 


0.695 


3750 


3710 


99 


90 








1.00 


0.777 


3510 


3190 


91 


91 








1.10 


0.849 


2890 


2520 


87 


92 








1.25 


0.965 


1880 
Av. 2910 


1750 
2820 


93 
97 


93 


1:3 


o-H 


5.75- 


0.70 


0.469 


2160 


2640 


122 


94 








0.80 


0.536 


4050 


4410 


109 


95 








0.90 


0.603 


4530 


4800 


106 


96 








1.00 


0.670 


4050 


3920 


97 


97 








1.10 


0.737 


3420 


3470 


101 


98 








1.25 


0.838 


2680 
Av. 3480 


2420 
3610 


90 
104 



10 Structural Materials Research Laboratory. 



Table 5.— Effect of Jigging on the Strength of Concrete. 
(Using aggregates of different size and grading.) 



Values from tests platted in Figs. 7 and 8. 

All cylinders were molded by the standard method before jigging on machine shown in Fig. 2. (100 r.p.m.; 

0.1-in. drop; jigged 20 sec.) 
Compression tests of 6 x 12-in. cylinders. 
Age at test 28 days; stored in damp sand; tested damp. 
Aggregates— Sand and pebbles from Elgin, 111., except where otherwise noted. 
Each value is the average of 5 tests made on different days. ■ 

Variation in grading in last two groups was produced by mixing different percentages of sand and coarse 

aggregate. 







Aggregate. 




Water- 
Ratio to 


Compressive Strength. 


Ref. 


Mix 
by 
Vol. 






Relative 
Consist- 




Standard 


Jigged 


No. 


Size. 


F.M. 


Volume of 


Standard Method, 


Method Plus 


Concrete, 




ency. 


Cement. 


lb. per sq. in. 


Jigging, lb. per 


Per cent of 
















sq. in. 


Standard. 


123 


1:5 


0-28 


1.20 


1.00 


1.410 


360 


400 


Ill 


124 




0-14 


2.25 




1.290 


510 


580 


114 


125 




0-8 


2.64 




1.245 


500 


650 


130 


'126 




0-4 


3.06 




1.195 


950 


1060 


112 


127 




0-1 


4.04 




1.080 


1540 


1270 


82 


128 




0-f 


5.02 




0.960 


2290 


2060 


90 


84 




o-ij 


5.75 




0.875 


2840 


2630 


93 


129 


1:3 


0-28 


1.20 


1.00 


0.990 


680 


860 


126 


130 




0-14 


2.25 




0.920 


1060 


1360 


128 


131 




0-8 


2.64 




0.890 


1520 


1720 


113 


132 




0-4 


3.06 




0.860 


2080 


2020 


97 


133 




o-f 


4.04 




0.790 


3050 


2930 


96 


134 




o-.f 


5.02 




0.720 


3840 


3420 


89 


96 




o-u 


5.75 




0.670 


4050 


3920 


97 


47 


1:5 


0-1* 


4.00 


1.00 


1.085 


1450 


1460 


101 


48 






5.00 




0.960 


2160 


1960 


91 


49 






5.50 




0.910 


2500 


2250 


90 


50 






5.75 




0.875 


2980 


2360 


79 


51 






6.00t 




0.845 


2710 


2630 


97 


52 






6.25t 




0.810 


2610 


2520 


96 


53 






6.50f 




0.785 


2110 


2010 


95 


54* 


1:5 


0-1* 


4.00 


1.00 


1.085 


1180 


1390 


118 


55* 






5.00 




0.960 


2030 


1850 


91 


56* 






5.50 




0.910 


2450 


2290 


93 


57* 






5.75 




0.875 


2630 


2430 


92 


58* 






e.oot 




0.845 


2420 


2500 


103 


59* 






6.25t 




0.810 


1960 


1760 


90 


60* 






6.50f 




0.785 


1550 


1460 


94 



* Crushed limestone for coarse aggregate. 

t These aggregates are too coarse for the quantity of cement used. See discussion on page 15. 
Bulletin 1, "Design of Concrete Mixtures," Structural Materials Research Laboratory. 



Effect of Vibration, Jigging and Pressure on Concrete. 11 



Table 6. — Effect of Jigging on the Strength of Concrete. 

All cylinders were molded by the standard method before jigging on machine shown in Fig. 2. 

Compression tests of 6 x 12-in. cylinders. 

Age at test 2S days; stored in damp sand; tested damp. 

Aggregates — Sand and pebbles from Elgin, 111. (graded 0-U in.). 

Each value is the average of 5 tests made on different days. 



Ref. 
No. 



Mix 

by 

Volume. 



F.M. 

of 
Aggre- 
gate. 



Relative 
Consist- 
ency. 



Water- 
Ratio 
to Volume 
of Cement. 



Compressive 
Strength. 



lb. per 
sq. in. 



Per cent of 
Standard. 



Treatment of Concrete. 



Effect of Height of Drop. 100 r.pan., for 20 sec. (See Fig. 9). 



31,51,84 


1:5 


5.75 


1.00 


0.875 


2780* 


100 


Standard method of molding. 


17 










2340 


84 


Drop . 02 in. 


18 










2480 


89 


Drop . 05 in. 


19 










2250 


81 


Drop . 10 in. 


20 










2520 


91 


Drop .20 in. 


21 










2640 


95 


Drop .30 in. 


22 










2460 


88 


Drop .50 in. 



Effect of Rate of Jigging, 0. 1-in. drop, for 20 sec. (See Fig. 10). 



31,51,84 


1:5 


5.75 


1.00 


0.875 


2780* 


100 


Standard method of molding. 


12 










2640 


95 


Jigged at 30 r.pjn. 


13 










2490 


90 


Jigged at 50 r.p.m. 


14 










2470 


89 


Jigged at 75 r.p.m. 


15 










2520 


91 


Jigged at 100 r.p.m. 


16 










2420 


87 


Jigged at 150 r.pan. 



Effect of Time Jigged at 100 r.p.m., 0.1-in. drop (See Fig. 11). 



31,51,84 


1:5 


5.75 


1.00 


.875 


2780* 


100 


Standard method of molding. 


32 












2440 


88 


Jigged for 5 sec. 


33 














2260 


81 


Jigged for 10 sec. 


34 














2390 


86 


Jigged for 20 sec. 


35 














2320 


83 


Jigged for 30 sec. 


36 














2251 


81 


Jigged for 45 sec. 


37 














2190 


79 


Jigged for 1 min. 


38 














2090 


75 


Jigged for 2 min. 


39 










2170 


78 


Jigged for 3 min. 



Miscellaneous Jigging Tests, 100 r.p.m., 0. 1-in. drop, jigged 20 sec. (See Fig. 12). 



31,51,84 


1:5 


5.75 


1.00 


.875 


2780* 


100 


Standard method of molding. 


40 










2780 


100 


Standard method of molding, 
jigged with 30-lb. weight on 
top. (See Figs. 9, 10 and 11.) 


15,19,34 










2390 


86 


Jigged immediately. 


41 
















2550 


92 


Stood 1 hr. before jigging. 


42 
















2940 


106 


Stood 2 hr. before jigging. 


43 
















2950 


106 


Stood 3 hr. before jigging. 


44 
















3000 


108 


Stood 4 hr. before jigging. 


45 
















28701 


103 


Stood 6 hr. before jigging. 


46 
















2770 


100 


Molded by standard method 
















on jigging machine while in 
















operation. 



• Average of 15 tests made on different days. See Table 2. 



12 Structural Materials Research Laboratory. 



Table 7. — Effect of Pressure ox the Strength of Concrete. 

All cylinders were molded by standard method before pressure was applied. Pressures higher than 
50 lb. per sq. in. were applied by a testing machine, as shown in Fig. 3. 



Ref. 

No. 



Mix 

by 
Volume. 


F.M. 

of 
Agg. 


Relative 
Consist- 
ency. 


Water-Ratio. 


Compressive 
Strength. 


As 
Mixed. 


After 
Pressure. 


lb. per 
sq. in. 


Per cent 
of Stand- 
ard. 



Treatment of Concrete. 



Pressure Applied 15 Minutes. 



31,51,84 


1:5 


5.75 


1.00 


0.875 


0.875 


2780* 


100 


Standard method of molding. 


23 












0.842 


3140 


113 


Pressure, 2 lb. per sq. in. 


24 














0.845 


3000 


108 


5 lb. per sq. in. 


25 














0.831 


2930 


105 


10 lb. per sq. in. 


26 














0.816 


2900 


104 


" 25 lb. per sq. in. 


27 














0.820 


3130 


113 


" 50 lb. per sq. in. 


28 














0.810 


3470 


125 


" 100 lb. per sq. in. 


29 














0.785 


3360 


121 


" 200 lb. per sq. in. 


30 














0.751 


3590 


129 


" 500 lb. per sq. in. 










Av. 


0.819 


3150 


113 





Pressure Applied 1 Hour. 



31,51,84 


1:5 


5.75 


1.00 


0.875 


0.875 


2780* 


100 


Standard method of molding. 


23 










0.845 


2920 


105 


Pressure, 2 lb. per sq. in. 


24 










0.824 


2830 


102 


5 lb. per sq. in. 


25 










0.839 


2950 


106 


" 10 lb. per sq. in. 


26 










0.834 


2880 


104 


" 25 lb. per sq. in. 


27 










0.821 


3120 


112 


" 50 lb. per sq. in. 


28 










0.810 


3190 


115 


" 100 lb. per sq. in. 


29 










0.781 


3790 


136 


" 200 lb. per sq. in. 


30 








Av. 


0.756 
0.820 


3470 
3100 


125 
112 


" 500 lb. per sq. in. 



Pressure Applied 4 Hours. 



31,51,84 


1:5 


5.75 


1.00 


0.875 


0.875 


2780* 


100 


Standard method of molding. 


23 










0.855 


2880 


104 


Pressure, 2 lb. per sq. in. 


24 










0.845 


2980 


107 


5 lb. per sq. in. 


25 










0.820 


3200 


115 


" 10 lb. per sq. in. 


26 










0.840 


2900 


104 


" 25 lb. per sq. in. 


27 










0.821 


2990 


" 108 


" 50 lb. per sq. in. 


28 










0.795 


3270 


118 


" 100 lb. per sq. in. 


29 










0.767 


3350 


121 


200 lb. per sq. in. 


30 








Av. 


0.750 
0.819 


3680 
3120 


132 

112 


" 500 lb. per sq. in. 



Pressure Applied 16 Hours. 



31,51,84 


1:5 


5.75 


1.00 


0.875 


0.875 


2780* 


10Q 


Standard method of molding. 


23 










0.834 


3060 


110 


Pressure, 2 lb. per sq. in. 


24 










0.824 


2710 


97 


5 lb. per sq. in. 


25 










0.815 


2630 


95 


" 10 lb. per sq. in. 


26 










0.846 


2670 


96 


" 25 lb. per sq. in. 


27 










0.798 


3320 


119 


" 50 lb. per sq. in. 


28 










0.795 


3330 


120 


" 100 lb. per sq. in. 


29 










0.794 


3410 


123 


" 200 lb. per sq. in. 


30 








Av. 


0.766 
0.816 


3420 
3040 


123 
109 


" 500 lb. per sq. in. 



Effect of Vibration, Jigging and Pressure on Concrete. 13 



Table 7. — Continued. 



Ref. 
No. 



Mix 
by 

volume. 



F. M. 

of 

Agg, 



Relative 
Consist- 
ency 



Water-Ratio 



As 
Mixed. 



After 
Pressure. 



Compressive 
Strength 



lb. per 
sq. in. 



Per cent 
of Stand- 
ard. 



Treatment of Concrete. 





Grand Average of all Times of Application of Pressure (See Figs. 13 to 16). 


31,51,84 


1:5 


5.75 


1.00 


0.875 0.875 


2780* 


100 


Standard method of molding. 










| 0.844 


3000 


108 


Pressure, 2 lb. per sq. in. 










1 0.834 


2880 


104 




5 lb. per sq. in. 










0.826 


2930 


105 




10 lb. per sq. in. 










0.834 


2840 


102 




25 lb. per sq. in. 










0.815 


3140 


113 




50 lb. per sq. in. 










0.802 


3320 


119 




100 lb. per sq. in. 










| 0.782 


3480 


125 




' 200 lb. per sq. in. 










| 0.756 


3540 


127 


" 500 lb. per so., in. 



Average of 15 tests made on different days, see Table 2. 



6000 




/OOO 



S^e*/- -S77/S7. 0.//S7. &S-0/&. 

i j I 



.70 ,&0 .90 WO /JO 

/Peh-f/ve Consistency 



/.?0 



/JO 



FIG. 5. — EFFECT OF CONSISTENCY ON THE STRENGTH OF JIGGED CONCRETE. 
Specimens molded by standard method and parallel sets jigged on machine shown in Fig. 2. 
Compression testa of 6 x 12-in. cylinders. Age 28 days. Data from Table 4. 



Structural Materials Research Laboratory. 
/SO 









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It 



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J/rff^rf ?0 ttr. 
















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* 90 

.70 JS .ffO .S5 .90 35 /.OO /<T //O //S /.PO /?£ 

/?e/otive Cor?s/sfer?cy 

. 6. — EFFECT OF CONSISTENCY ON THE STRENGTH OF JIGGED CONCRETE- 
Each value is the average of 20 tests, 5 each from 4 different mixes in Table 4. 

sooo 



% 

I 

X 

\ 

<3 



FIG, 



4000 



sooo 



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fv/7e/7<?ss Mcxy^y/cvs ofs1<?jsr<s£?af& 



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7. EFFECT OF SIZE OF AGGREGATE ON THE STRENGTH OF JIGGED CONCRETE 

Compression tests of 6 x 12-in. cylinders. Age 28 days. Data from Table 5. 



Effect of Vibration, Jigging and Pressure on Concrete. 15 

indicate that hand-puddling (if thoroughly done) is just as effective as 
vibration in placing concrete. In other words, concrete which completely fills 
the form is not improved by vibration. This should not be construed as 
meaning that vibration is not effective in causing concrete to find its way into 
intricate form work and around the reinforcing bars. 

The effect of jigging is shown in Tables 4 to 6, and Figs. 5 to 12. The 
jigging method used was one which would be applicable to concrete products 
plants. The tests show that in general jigging of concrete which has been 
placed by puddling is injurious to the strength. The improvement for the 
small-sized aggregates is probably due to the fact that the puddling method 
is not so satisfactory for this condition. 

In comparing the tests of crushed limestone and pebbles in Table 5 it 
should be noted that the three coarsest gradings in each group (fineness 
modulus 6.00 and over) are too coarse for this mix, consequently the con- 
crete strengths fall off. The extremely coarse mixtures cause a much greater 
reduction in the strength of the concrete made from crushed stone than from 
gravel. For this reason it is not proper to draw conclusions from a com- 
parison of average values from the two types of coarse aggregate. If we 
confine our attention to the ordinary range in aggregate grading (fineness 
modulus 5.00 to 5.75) we find little difference in strength of concrete from 
the two materials. For these conditions the average strength with pebbles 
is 2550 lb. per sq. in. for the standard method of hand-puddling and 2190 
after jigging; corresponding values for crushed stone are 2370 and 2190 lb. 
per sq. in. 

The tests of concrete setting under pressure are of interest in that they 
reveal the reason for increased strength due to this treatment. The concrete 
strength is increased due to the fact that some of the original mixing water is 
forced out. The higher the pressure, the more water is removed, hence the 
higher the strength. 

Attention is called to the unusual uniformity of the results of the tests 
in this series, as illustrated by the fact that in the diagrams the points 
fall on smooth curves. There are only a few instances in which there is 
any appreciable -deviation from this rule. 

Summary and Conclusions. 

The tests gave conclusive results on many phases of the effect of vibration, 
jigging and pressure. In some instances the effect is entirely different from 
what accepted opinion would suggest. Following is a brief summary of the 
tests: 

Effect of Puddling and Tamping (Table 2). 

1. Varying the number of strokes from 12 to 50 on each 4-in. layer in the 
standard method of hand-puddling with a f-in. bar had little influence on the 
compressive strength of ordinary plastic concrete. 

2. In general, the tamping methods used gave lower strengths than 
hand-puddling. 

3. A tamper of large diameter for a given weight was less effective than 
one of small diameter. 



16 Structural Materials Research Laboratory. 

4. Increasing the thickness of the layer from 4 to 6 in. caused a falling-off 
in strength of about 12 per cent for tamped concrete. 

5. Tamping or puddling the first 4-in. layer only, caused a falling off in 
strength of 10 to 13 per cent. 

6. Striking the metal form with a steel bar after the completion of molding 
by standard method had no effect on the strength of concrete. 



^ 4000 




\eooo 

\ 

k 

^ /ooo 

\ 

I 



%^^S^y7^<y^cy^^7(eS/b/7iP^ 0//sz (Jra^ 



4.00 <ZS0 j:00 ^7jT<? 6.0O 6.SO 

FIG. 8. EFFECT OF GRADING OF AGGREGATE ON THE STRENGTH OF 

JIGGED CONCRETE. 

Specimens molded by standard method and parallel sets jigged on machine shown in Fig. 2. 
Compression tests of 6 x 12-in. cylinders. 1 : 5 mix. Age, 28 days. All aggregate^ graded 
0-1}^ in. Data from Table 5. 

7. The "standard" method of hand-puddling using 25 strokes with a 
f-in. steel bar for each 4-in. layer of concrete in a 6 x 12-in. cylinder is recom- 
mended for laboratory tests of concrete. 



Effect of Vibration with Electric Hammer. 
8. Vibration of the specimen after molding by means of an electric 
hammer running at 1000 r.p.m. had little influence on the strength of the 
puddled concrete up to "a period of about 30 seconds. If continued, there 
was a steady falling off in strength; after 45 to 60 seconds the strength was 
only 90 "per cent, of that produced by the standard method of puddling. 
(Table 3, and Fig. 4). 



Effect of Vibration, Jigging and Pressure on Concrete. 17 






sooo t 



x 

\ 

•I 

I 

r 



iS ^ 

























%Y&0/& wrf 0/7/0/? ofc/Z/s?^/' 










/OO tyt-O/CZS /£>&/- S77//7. 



























O .OS JO ./s *PO .<PS .JO .JS 40 ^s .so 

/?/~0/D - /S7C/?&S 



FIG. 9. EFFECT OF HEIGHT OF DROP IX JIGGING TESTS. 

Compression tests of 6 x 12-in. cylinders. Age 28 days. Data from Table 



^ 4000 




I 

ft /ooo 

1 



V3 



S r /£ > cr/o/ r Je?g/sx?. 
rfppeof <rV see. 
O///7, c/ro/?. 



O PS SO 7S /OO /PS /SO 



FIG. 10. — EFFECT OF RATE OF JIGGING ON THE STRENGTH OF CONCRETE. 
Compression tests of 6 x 12-in. cylinders. 1 : 5 mix. Age 28 days. Data from Table 6. 



18 Structural Materials Research Laboratory. 



4000 



\ 

i 

^ POOO 

X /ooo 

\ 

\ 



< ) &SO/&. w£ '0/7 /o/P of * cy/Zsioter- 
o 




<9.//>7. &t~o/? 



<? PS SO 7S /OO /PS /SO /7S POO 
7frr?e of J/^rt<p-seco/7cfe 

FIG. 11. — EFFECT OF DURATION OF JIGGING ON THE STRENGTH OF CONCRETE. 
Compression tests of 6 x 12-in. cylinders. 1 : 5 mix. Age. 28 days. Data from Table 6. 




/OO tfrOyDS /D&/- S77/S7. 

0.///7. c/y^o/?* 



J 



s 



/?<?& os^ ^bsrcr&fe ^?<s>/2>^^ ^?ip>p//7<p —/7<o<y/~*s 

FIG. 12. — EFFECT OF AGE OF CONCRETE BEFORE JIGGING. 
Compression tests of 6 x 12-in. cylinders. '1:5 mix. Age, 28 days. Data from Table 6.[ 



Effect of Vibration, Jigging and Pressure on Concrete. 19 

Effect of Jigging. 

9. In general, jigging in any manner with the apparatus used reduced 
the compressive strength of the concrete regardless of the height of drop, 
rate or duration of treatment. Exceptions were found in the dry mixes and 
those made of aggregates of the smaller sizes. (Tables 4 to 6; Figs. 5 to 12.) 

10. There was little difference in the effect of jigging due to the quantity 
of cement used. (Fig. 5.) 



\ 



\ 



/ooo 



Cj 



















r ° 


&*?& 


r/o/ r /= > / 


-<?&S{S/~& 

























/OO <rV0 SOO 40O 



soo 



FIG. 13. — EFFECT OF PRESSURE ON THE STRENGTH OF CONCRETE. 
Compression tests of 6 x 12-in. cylinders. 1 : 5 mix. Age, 28 days. Pressure applied im- 
mediately after molding. Each point represents the average of 20 tests, 5 each from 4 
different times of application of pressure ranging from 15 min. to 16 hr. Data from Table 7 



11. In the very dry mixes the strength, due to jigging for 20 seconds, was 
increased about 25 per cent. (Figs. 5 and 6.) 

12. The wetter mixes (relative consistency 1.10 to 1.25) were reduced in 
strength 3 to 6 per cent by jigging. (Figs. 5 and 6.) 

13. Pebbles and crushed limestone as coarse aggregate gave essentially 
he same results in the jigging tests. (Fig. 8.) 

14. The concretes from the finer aggregates showed a material increase 
in strength with jigging in both 1 : 5 and 1 : 3 mixes. (Fig. 7.) 

15. For aggregate coarser than about f in., jigging reduced the strength 
from 3 to 10 per cent. (Fig. 7.) 



20 Structural Materials Research Laboratory. 

16. The grading of the aggregates (for a given maximum size) had little 
influence on the effect of jigging. (Fig. 8.) 

17. The greater the drop the greater the reduction in strength for 1:5 
concrete. For a drop of \ in. the strength was reduced 12 per cent. (Fig. 9.) 



4000 



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£ POOO 

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\ 



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o 



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7//77&-/70£/y^S 



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FIG. 14. — EFFECT OF DURATION OF PRESSURE ON THE STRENGTH OF CONCRETE. 

Compression tests of 6 x 12-in. cylinders. 1 : 5 mix. Age, 28 days. Pressure applied immedi- 
ately after molding specimen. Each point represents the average of 45 tests, 5 each from 
9 different pressures ranging from 2 to 500 lb. per sq. in. Data from Table 7. 



18. The faster the rate of jigging the lower the strength of 1:5 concrete. 
Using 1^-in. aggregate at 150 r. p. m. the strength was reduced about 13 per 
cent. (Fig. 10.) 

19. The strength of 1:5 concrete fell off rapidly with the duration of 
jigging. After 2 to 3 minutes jigging the strength was reduced about 20 per 
cent, as compared with standard method of hand-puddling. (Fig. 11.) 

20. Allowing the concrete to stand for a period of time before jigging, 
increased the strength to a slight extent. The maximum increase was found 
at 2 to 4 hr. (Fig. 12.) 



Effect of Vibration, Jigging and Pressure on Concrete. 21 

21. The application of a pressure of 1 lb. per sq. in. during the jigging 
process (equivalent to a head of 1 ft. of fresh concrete) gave the same strength 
as standard hand-puddling. (Figs. 9, 10 and 11). 

22. Molding the cylinders by the standard method on the jigging table 
while it was in motion, gave the same strength as standard hand-puddling 
without jigging. (Table 6.) 

/OO 



70 



\ 

> .CO 

X *> 

SO 



o /OO POO soo 400 ^oo 

FIG. 15.— WATER-HATIO OF CONCRETE AFTER PRESSURE. 

Each point represents the average of 20 tests, 5 each from 4 different times of application of 
pressure. Data from grand average values in Table 7. 















































/v 


c 






f/bs? 











































Effect of Pressure. 

23. The compressive strength of concrete was increased by pressure 
applied immediately after molding. For pressure of 200 to 500 lb. per sq. in. 
the increase was. 20 to 35 per cent. (Fig. 13). 

24. The duration of pressure as between 15 min. and 16 hr. produced no 
difference in strength. (Fig. 14.) 

25. There was a steady reduction in the water-ratio of the concrete with 
the application of pressure. (Fig. 15.) 



22 



Structural Materials Research laboratory. 



26. The application of pressure increased the strength of concrete in 
accordance with the quantity of mixing water expelled. (Fig. 16.) 

27. The tests of concrete subjected to pressure showed the usual relation 
between compressive strength and water-ratio. The strength is increased 
because the water is expelled. In other words, pressure produces a drier concrete, 
and consequently gives higher strength. * This makes it clear why the duration 
of pressure has no influence on the result. 



r 

X 



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SOOO 



POOO 



/ooo 



■*■*— ••^^ o 



7S 76 77 7S 79 -&0 .a/ •&? .6>J -&? &S 



FIG. 16. — EFFECT OF QUANTITY OF MIXING WATER ON THE STRENGTH 
OF CONCRETE. 
Compression tests of 6 x 12-in. cylinders. Age, 28 days. Water-ratio determined after 
application of pressure. Each point represents the average of 45 tests, 5 each from 9 
different pressures. Data from grand average values in Table 7. The narrow range in 
water-ratio gives a straight line relation for these tests. The water-strength relation is 
represented by a curved line as shown in Bulletin 1, Structural Materials Research Labo- 
ratory. 



Further Discussion of Vibration, Jigging and Pressure Tests. 

The indications of the vibrations and jigging tests should not be mis- 
interpreted. The tests show that after the concrete is properly placed these 
methods of treatment do no good and may be harmful if too severe or too 
long continued. However, there can be no doubt of the value of such methods 

* For effect of consistency on the strength of concrete, see Bulletin 1 referred to above; and "Effect of 
Time of Mixing Concrete," Proceedings, American Concrete Institute, 1918. 



Effect of Vibration, Jigging and Pressure on Concrete. 23 

for getting concrete into place in intricate forms and around reinforcing bars. 
The tests are of value in showing that this is the only desirable function of 
such treatments. The tests under Ref. No. 149 (Table 2) show the ill effects 
of lack of compactness in the concrete. Here the strength was reduced 13 
per cent due to failure to tamp or puddle the top 9 in. of the cy Under. It 
is impracticable to duplicate in a compression test piece the performance of air 
hammers and other similar methods of vibrating when used on reinforced 
concrete work. 

v The tests show that with jigging high strength may be secured with drier 
mixes than would be feasible otherwise. It is a matter of common experience 
that concrete of drier consistency (and consequently higher strength) can be 
placed by means of jigging or vibration than would be possible by the usual 
methods. 

The roller method of finishing concrete roads, walks and floors is an 
interesting example of a combination of- slight vibration and pressure 
accompanied by the removal of excess water. Transverse tests on con- 
crete made in this Laboratory showed a marked increase in strength of the 
rolled slabs as compared with similar slabs without rolling.* 

It is clear from these tests that if tamping, vibration or pressure on 
fresh concrete are to be effective in increasing its strength three factors 
must be kept in mind: 

(1) We must take advantage of the fact that with these methods 
the concrete can be placed and finished dryer than with ordinary 
methods. 

(2) Excess water which is brought to the surface must be 
removed. 

(3) We must take advantage of the fact that aggregate of a 
coarser grading may be used when such methods are employed than 
would be practicable otherwise. 

The advantages to be gained under (3) are due to the fact that up to 
a certain point a plastic mix can be secured with a smaller quantity of 
water if the aggregate is as coarse as practicable. Unless these precautions 
are taken, tamping and vibration are of doubtful value. 

* See paper of A. N. Johnson, Proc. Am. So. Testing Materials, 1917, Part II, p. 378. 



LIST OF PUBLICATIONS OF THE 
STRUCTURAL MATERIALS RESEARCH LABORATORY 



Bulletin 1 — Design of Concrete Mixtures. 

Bulletin 2 — Effect of Curing Condition on the Wear and 
Strength of Concrete. 

Bulletin 3 — Effect of Vibration, Jigging and Pressure on Fresh 
Concrete. 

Circular 1 — Colorimetric Test for Organic Impurities in Sands. 

Effect of Time of Mixing on Strength of Concrete. 



LIBRARY OF CONGRESS 

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